Method for producing polymer-bonded 2-chlorotrityl-chloride

ABSTRACT

The invention relates to a method for producing polymer-bonded 2-chlorotrityl chloride of formula (I), wherein P means a polymer support, preferably cross-linked polystyrene, by reacting a corresponding carboxylic acid with hydrogen chloride. The method enables the support resin from the solid-phase peptide synthesis produced after the splitting-off of the peptide to be re-used.

[0001] The invention relates to a process for the preparation of polymer-bound 2-chlorotrityl chloride of the formula

[0002] in which the symbol

[0003] is a polymeric support and preferably a crosslinked polystyrene resin.

[0004] Polymer-bound 2-chlorotrityl chloride is a commercially obtainable (Calbiochem-Novabiochem AG, Läufelfingen, Switzerland, Product No. 01-64-0021) reagent for the solid-phase synthesis of peptides. It is reacted here firstly with an N-protected amino acid, which forms the C-terminus of the peptide to be synthesized, to give the corresponding trityl ester. After synthesis of the peptide chain, the peptide is cleaved by treatment with a carboxylic acid, for example dilute trifluoroacetic acid or acetic acid, the corresponding polymer-bound trityl ester of the formula

[0005] in which R is a C₁₋₄-alkyl or C₁₋₄-haloalkyl group and preferably methyl or trifluoromethyl being formed. The resin is thus consumed and can no longer be employed for further syntheses in this form.

[0006] C₁₋₄-Alkyl is to be understood here and below as meaning all alkyl groups having 1 to 4 carbon atoms, that is methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl and tert-butyl. C₁₋₄-Haloalkyl is correspondingly to be understood as meaning all C₁₋₄-alkyl groups having one or more identical or different halogen atoms as substituents, preferably perfluorinated C₁₋₄-alkyl groups such as trifluoromethyl.

[0007] The object of the present invention was therefore to make available a process which regenerates the polymer-bound 2-chlorotrityl chloride again from the acyloxylated resin (II) formed after cleavage of the peptide, which can then be used again for peptide syntheses.

[0008] According to the invention, this object is achieved by the process according to claim 1.

[0009] It has been found that by simple treatment of the acyloxylated resin (II) with hydrogen chloride in an organic solvent the polymer-bound 2-chlorotrityl chloride (I) can be regenerated. Since the replacement of carboxylate by chloride is obviously an equilibrium reaction, the treatment is advantageously repeated a number of times using fresh solvent in order to remove the released carboxylic acid from the system and thus to achieve a complete replacement. It is also possible to percolate a packing of the acyloxylated resin (II) with a solution of hydrogen chloride until the carboxylate is completely replaced by chloride.

[0010] A suitable solvent is fundamentally any anhydrous organic solvent which does not react with hydrogen chloride and has an adequate solvent power for this. Preferably, dichloromethane is employed as the solvent.

[0011] The process according to the invention can be carried out both using a prepared solution of hydrogen chloride and using a solution produced in situ by passing gaseous hydrogen chloride into a reactor charged with the solvent and the acyloxylated resin (II).

[0012] The following example clarifies the implementation of the process according to the invention, without a restriction being seen therein.

EXAMPLE

[0013] 5 g of trifluoroacetoxylated resin (II) were added to a double-jacketed reactor for solid-phase peptide synthesis (cylindrical glass vessel having a temperature-controlled jacket and glass frit in the lower part) and treated with 20 ml of dichloromethane. Nitrogen was firstly passed through the frit for 10 min and the arrangement was cooled to 5° C. A gentle stream of hydrogen chloride was then passed through the frit, the excess hydrogen chloride escaping from the reactor being absorbed in wash bottles containing sodium hydroxide solution. After about 10 min, the solution was filtered off with suction and replaced by fresh dichloromethane. Hydrogen chloride was then again passed in for about 10 min. This process was carried out a total of five times. The resin was then filtered off with suction under nitrogen and dried overnight at 30° C. The polymer-bound 2-chlorotrityl chloride thus obtained exhibited no significant differences in the binding capacity for amino acids to the commercially obtainable product. 

1. Process for the preparation of polymer-bound 2-chlorotrityl chloride of the formula

in which

is a polymeric support, preferably crosslinked polystyrene, characterized in that the corresponding carboxylic acid ester of the formula

in which R is a C₁₋₄-alkyl or C₁₋₄-haloalkyl group, is treated with a solution of hydrogen chloride in an organic solvent.
 2. Process according to claim 1, characterized in that R is methyl or trifluoromethyl.
 3. Process according to claim 1 or 2, characterized in that the organic solvent used is dichloro-methane.
 4. Process according to claims 1 to 3, characterized in that the treatment is repeated a number of times with fresh solution.
 5. Process according to one of claims 1 to 4, characterized in that the solution of hydrogen chloride in the organic solvent is prepared in situ by passing in hydrogen chloride gas.
 6. Process according to one of claims 1 to 3, characterized in that a packing of the polymer-bound carboxylic acid trityl ester (II) is percolated with the solution of hydrogen chloride in the organic solvent. 